No one else rides him other than me. I have previously tried to ride him out with other horses but he tends to play up even more. The first time I rode him out in company with a quiet horse and he bucked non-stop after riding for 10 mins! I've had his tack checked but not his back yet. Thanks for the tips though

I would never recommend getting off a horse which is wound up while hacking - there's a good chance he'll run for it then you've lost him! If he's started playing up in the school also i would get his back/saddle fit checked. The way I normally cope with horses who get excited when hacking is to find a really steady companion to ride out with. Get your horse used to walking sidebyside with the other horse in a school environment - once he's happy with that move to on the road then gradually onto bridleways - never letting him get above a walk and never tensing or trying to hold him back with your hand (fight the impulse!) - if he tries to tank off push him behind the other horse. You may also find that if you find somewhere where you can safely let him go at a flat out gallop that may help - if he tries to buck during this just push him forwards as fast as he'll go - it'll reduce the novelty factor! Good luck!